The present invention is directed to a rhythm apparatus for an electronic musical instrument. In prior art systems, an instrument player could select any standard well-known rhythm pattern such as a waltz, mambo or the like and one of a plurality of unpitched musical instrument sounds to be simulated with the selected rhythm pattern. The standard rhythm patterns were predetermined and fixed in a rhythm matrix unit well-known in the prior art so that the instrument player could not alter or vary these rhythm patterns. This type of rhythm apparatus did not provide for any degree of creativity or flexibility by the instrument player to select different rhythm patterns or to alter the standard patterns. Furthermore, the fixed rhythm units required a great amount of storage for the numerous standard rhythm patterns available.